Effect of a biocide treatment on microbes in sweet sorghum juice

Authors: Wright, Maureen

Submitted to: African Journal of Agricultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/10/2017
Publication Date: 3/30/2017
Citation: Wright, M.S. 2017. Effect of a biocide treatment on microbes in sweet sorghum juice. African Journal of Agricultural Research. 12(13):1074-1078.

Interpretive Summary: Sweet sorghum has potential as a feedstock for bioproducts production due to its ability to grow in marginal soils that are low in moisture and fertilization. The return on the financial investment in equipment used to collect and process juice from sorghum stalks can be enhanced by extending processing past harvest season. A limitation of storing sorghum juice for delayed processing is the degradation of sugar in the juice. Degraded sugars are no longer available for fermentation into bioproducts. Microbes in the environment are a source of sugar degradation. Sugarcane juice is treated with biocides to inhibit microbial growth during processing. A biocide used in sugarcane mills was tested here for the ability to control microbial growth in sorghum juice. While the biocide can be very effective against some microbes, the data in this study show that it was not effective across the full range of contaminating microbes and suggests that a combination of biocides will be necessary to prevent sugar degradation.

Technical Abstract: Sweet sorghum is a feedstock for conversion to bioproducts, due to its fermentable sugar content and tolerance of environmental conditions such as heat and drought. Microbial contamination of sweet sorghum juice can result in loss of fermentable sugars. Biocidal chemicals are used with other sugar-producing crops to control microbial growth. A carbamate-based biocide used in the sugarcane industry was applied to sorghum juice collected from 4 in and 8 in billets, or whole stalks, and growth of microbes was evaluated. Dosing with 200ppm biocide reduced the microbial count in juice samples by between 98.7% and greater than 99%, but a residual microbial count remained with to potential to consume sugars in the juice. Increasing the dose to 400ppm did not eliminate microbial contamination, with a growth reduction of 85.7% or less. Some of the contaminating microbes were identified as spore-formers, which enhances their ability to survive microbicides.